In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the complexity of the electrical and drive systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles. Such alternative fuel vehicles typically use an electric motor, perhaps in combination with another actuator, to drive the wheels.
Traditional motor control systems normally include a feedback device or position sensor, such as a resolver or encoder, to provide speed and position information about the motor. Feedback devices and associated interface circuits increase the costs of a motor control system, and these costs may become undesirable in high volume applications such as the production of automobiles. Additionally, a position sensor and its associated wiring harness increase the complexity and assembly time of an electric drive system in a vehicle.
As production volumes of alternative fuel vehicles increase, manufacturers are increasingly striving to reduce costs and the number of parts of a vehicle. The removal of a feedback device for an electric motor control system significantly reduces the manufacturing costs of an alternative fuel vehicle.
Currently, electric and hybrid electric vehicles often utilize numerous electric motor control technologies, such as the vector control of electric motors. A vector motor control scheme is a computationally intensive motor control scheme that maps the phase voltages/currents of a three-phase motor into a two-axis coordinate system. The hardware used to excite an electric motor using a vector control scheme is typically a three-phase power source inverter with, for example, six power transistors that shape the output voltage to the motor. Vector control requires rotor position information, which is normally obtained via a feedback device or position sensor.
Recently, sensorless control algorithms have been developed that do not use a position or speed sensor but utilize the motor voltage (command to the inverter) and current (feedback from the current sensor) to estimate the motor position and speed. However, at the beginning of the operation or during the restart, the motor voltage information is not available without measuring the actual motor voltage.
In the case of a permanent magnet motor, it is sometimes possible to identify the motor position and speed by measuring the motor terminal voltage using the analog circuit if the motor speed is high enough. However, such a method is sometimes not favorable due to isolation and reliability issues.
Accordingly, it is desirable to provide an improved method and system for initiating the operation of an electric motor when a sensorless control algorithm is used. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.